I bet on what dhama said.  Bryce will save to the last folder that had been used as a save.  It may not necessarily be the same folder you default to when using "open" 

I've done it several times.  My daughter will goof around in Bryce and save something to her account.  I will later work on a scene and do a save.  When I go back to open it later, it is not in my account or pre-set folder but in hers. 

Once you find the file and move it or re-save it to a location you pick, Bryce will start saving to that location all the time.  Does this make sense?